The glutathione (GSH) system of Procambarus clarkii (P.c.), the American red crayfish, is used as a marker of the effects of Fenitrothion (FT) and Endosulfan (ES), organophosphorus and organochlorinated insecticides, respectively. This system has been shown to be sensitive to different heavy metals poisoning, thus it has a double interest as marker for environmental contamination and as a potential source of xenobiotics or their metabolites to humans, since it is being fished commercially. The GSH content of the organ decreased 24 h after treatment with FT. FT promotes a 2-fold induction of GSH S-transferase (GST) activity at 6 h which is followed by a decrease of it at 24 h. The latter coincides with the decrease in GSH content. GST activity increases again over the control values at 48 h. Only the initial increase in GST activity is coupled with an increase in gamma-glutamyl transpeptidase (transpeptidase activity) (gamma-GT) activity. ES promoted a discrete increase in GSH concentration at the same time as a 2-fold increase in GST activity, again coupled with an increase in gamma-GT activity. The GST induction observed at 6 h with FT and 24 h with ES showed concentration dependency up to 1/4 of the reported LC50 of both pesticides. Higher concentrations showed no further effects on GST activity. The coupled control of the expression of GST and gamma-GT in the hepatopancreas of P.c. is discussed.